The substrate for “the analytical sensor using optical characteristics” refers to substrates for Surface Plasmon Resonance (hereinafter referred to as “SPR”), surface-enhanced Raman scattering substrates, optical biosensor substrates, electrochemical sensor substrates, mechanical sensor substrates and SPM (Scanning Probe Microscope) sensor substrates, etc. Hereinafter, it is abbreviated to “the analytical sensor”.
Among them, the surface plasmon mainly used as an analytical sensor chip is the term referring to the vibration phenomenon of electron density proceeding along with the interface between the metal thin film and the dielectric material. The surface plasmon, which is an electromagnetic wave proceeding along with the interface between the metal and the dielectric material, is not propagated inside the dielectric material but is present only on the surface since the size of wave vector thereof is greater than the vector of light proceeding inside the dielectric material. Therefore, to excite the surface plasmon it is required to make the wave vector great.
As the means for enhancing the wave vector, the attenuated total reflection method utilizing the prism with a high refractive index is used. It utilizes the prism and the metal thin film coated on the prism, wherein the metal thin film should be thin so that the incident photons into the prism can be passed through the metal thin film. The surface plasmon can be excited only when the incident photons are entered into prism through the metal thin film at an angle greater than an angle of total reflection.
All the photons greatly incident at the angle of total reflection are absorbed on the interface between the metal thin film and the dielectric material at a specific angle due to the surface plasmon resonance. The surface plasmon resonance generates a strong electric field at the interface between the metal thin film and the dielectric material, which electric field is controlled only on the surface but is perpendicularly attenuated by an exponential function. The strength of electric field in such a case has a great value ten to hundred times the strength in case where the surface plasmon is not excited.
Since the surface plasmon is greatly varied depending on the shape and reflective index of the dielectric material contiguous to the metal thin film, such properties are utilized to study the surface plasmon band gap by the interface between the dielectric material having a periodic structure and the flat metal thin film. As examples of the application thereof, the sensor using diffraction grids is intensively limited with respect to the measuring parameters, as compared to the sensor using prisms. In order to complement such limitation, it can be seen that the incidence angle may be reduced by moving the incident light in the direction of surface to gradually increase a period of the diffraction grid.
Meanwhile, the surface plasmon resonance is very sensitive to the incidence angle and therefore, can also be used in the small diffraction grid structure. It is anticipated that such study can be greatly utilized for the information storage elements or the optical sensor such as optical microscope, etc.
FIG. 1 shows the structure of general SPR systems. Referring to FIG. 1, the surface plasmon is a collective vibration phenomenon of electrons generated on the surface of the metal thin film (100), and the surface plasmon wave generated therefrom is a kind of surface electromagnetic waves proceeding along with the interface between the metal thin film (100) and the dielectric material (104) contiguous thereto. In the arrangement for surface plasmon resonance, the surface plasmon resonance is generated from a specific incidence angle at which the wave vector of the Everdesont wave conforms to the wave vector of the surface plasmon on the interface between the metal thin film (100) and the prism (102).
A change in the properties of the surface plasmon resonance according to the thickness and properties of the dielectric material on the metal thin film (100) having a nanometer thickness is utilized in the SPR sensors. Accordingly, for using the SPR sensors as a biosensor the metal thin film is coated with a physiologically active substance to induce the production of a physiological specific reaction on the metal thin film. Such metal thin film substrate coated with biological substances is designated as the SPR sensor chip. In this case, in order to improve the sensitivity of SPR sensors the metal thin films with various shapes are prepared. In the prior art, as the method for arranging the silica nanoparticles on the solid substrate the methods including spin coating, dropping method for spreading and then drying the dispersed solution, etc. have been used. However, although such prior methods can prepare the thin film by simply arranging the silica nanoparticles on the solid substrate, they have the problems that it is difficult to use them as the procedures for mass-production of the thin film with a great area within a short period, and further, to prepare the uniform substrate having a high sensitivity.
More specifically, they have the problem of a reproducibility by producing either the multi-layer film or the mono-layer film depending on various procedure conditions in manufacturing the substrate with a spin coating, for example, spin speed, time, presence of air bubbles in the dispersed solution the uniformity, and further, there are difficulties in controlling the experimental conditions each time according to the particle size and the viscosity of the solution.
According to one method using the spin coating, for example, when the nanosphere lithography masks as a polystyrene nanosphere are prepared using the spin coating method, only a part of the area of the substrate thus prepared is formed as the mono-layer film (single layer) and the remaining part of the substrate is formed as the multi-layer film (double layer). Therefore, it can be seen that it is difficult to manufacture the uniform substrate which can be produced in a large scale with a great area [John C. Hulteen, David A. Treichel, Matthew T. Smith, Michelle L. Duval, Traci R. Jensen, and Richard P. Van Duyne, “Nanosphere Lithography: Size-Tunable Silver Nanoparticle and Surface Cluster-Arrays”, (J. Phys. Chem. B 1999, 103, 3854-3863)].
In case where the substrate is manufactured according to the dropping method, there are more problems as compared to the case where the spin coating method is used. Accordingly, it will be well known to a person having an ordinary knowledge in this technical field that the dropping method is substantially not utilized.
As the more effective, up-to-date method, a method, which can be said to be a confined convective assembly produced during the drying procedure has been known (Mun Ho Kim, Sang Hyuk In, and O Ok Park, “Rapid Fabrication of Two- and Three-Dimensional Colloidal Films via Confined Convective Assembly”, Adv. Funct. Mater. 2005, 15, 1329-1335). This method is a method in which the dispersed solution is introduced into a gap between the substrates positioned at a certain interval, for example, at a distance of 100 μm, and a solid substrate on one side is put thereon while forming the film of particles of the dispersed solution on said substrate. However, according to this method the thickness of the film is controlled depending on a speed to raise up the substrates, a concentration of the dispersed solution, etc., but in manufacturing the single layer film there may be no room for controlling of the multi-layer film and the void as partially produced, since the film of particles is formed by a force spontaneously generated under evaporation of water. Therefore, this method also has a difficulty in forming the single layer film with a great area in a large scale.
Meanwhile, Korean Registered Patent No. 10-0597280 discloses a method for attaching the nanomaterials, wherein said nanomaterials are stably dispersed in an organic solvent, the Langmuir-Blodgett film comprising the nanomaterials is formed from the resulting dispersion, and then, the nanomaterials of said LB film are transferred and attached to the holder. In said patent, it has been described that according to the method for transferring and attaching the carbon nanotube LB film to the holder with using the Langmuir-Blodgett method (LB method) the carbon nanotube-attached nanostructures, which can be manufactured by the general semi-conductor process, can be produced to allow the production of a SPM (Scanning Probe Microscope) probe capable of detecting various physical, chemical and biological signals. The Langmuir-Blodgett (LB) film refers to a thin film formed through dispersing the water-insoluble materials in the liquid phase on the water surface having a certain area, which phenomenon was first discovered by Benjamin Franklin. The principle thereof is that on the basis of the properties of the so-called amphiphilic material, i.e. the properties that one side has a hydrophobic functional group and the other side has a hydrophilic functional group, the materials are aligned in a certain orientation on the surface of water (water-air interface) to make the production of a thin film at a molecular level possible. Said registered patent attaches the carbon nanotubes to the SPM probes using such LB film
However, the method for attaching the nanomaterials by using the Langmuir-Blodgett method according to said registered patent make no mention of the metal thin film to be transferred to the nanostructures which are required to be used in preparing the analytical sensor chip. In addition, there is the problem that in applying the Langmuir-Blodgett method it is difficult to transfer as the single layer the nanoparticles to be used in preparing the analytical sensor chip to the substrate. Accordingly, there remains a need for the method capable of producing the nanostructure substrate comprising the metal thin film, which can be used in preparing the analytical sensor chip, with a great area in a large scale.